body {
    font-family: Arial, sans-serif;
    background: #f0f4f8;
    margin: 0;
    padding: 0;
}

.container {
    max-width: 900px;
    margin: 40px auto;
    background: white;
    padding: 30px;
    border-radius: 10px;
    box-shadow: 0 0 15px rgba(0,0,0,0.1);
}

h1 {
    text-align: center;
    color: #0b3d91;
}

form {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

input[type=text],
input[type=password],
input[type=number] {
    padding: 10px;
    font-size: 16px;
    width: 100%;
    box-sizing: border-box;
}

button {
    padding: 12px;
    background: #0b3d91;
    color: white;
    border: none;
    font-size: 16px;
    cursor: pointer;
}

button:hover {
    background: #09327a;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
}

th, td {
    padding: 10px;
    border: 1px solid #ccc;
    text-align: center;
}

th {
    background: #e0e7ff;
}

.error {
    color: red;
    margin-top: 10px;
}

.success {
    color: green;
    margin-top: 10px;
}

#subnet {
    height: 2.5em;          /* 两倍行高，1em ≈ 一行 */
    font-size: 18px;      /* 保持字体大小一致 */
    padding: 4px 8px;     /* 上下留一点呼吸空间 */
}